Based on given specs, what upgrade(s) will give me the most bang for my buck for ~$300?

[mkohanek]

I am wanting to upgrade my PC for gaming purposes. I am currently playing Elder Scrolls Online, and that is where I would like to see the better performance mainly. Though I do also play a lot of single player RPGs. I usually stay fairly steady at right over 30 fps, with it getting down to the 20s and occasionally 10s when there is a lot going on on-screen.
I run at fairly high settings right now (max draw distance, medium shadows, most everything else high or max). My goal is to run highest settings I can at a nice steady >45 fps frame rate. The closer to 60 the better.

So let's say within the range of $300, what would you suggest I upgrade or change to gain the most noticeable improvements. No need to consider that a "hard" $300 limit, just a ballpark.

Here is what I have right now:

MOTHERBOARD - ASUS M4A89TD PRO/USB3 AM3 AMD 890FX
CPU - AMD Phenom II X6 1090T Black Edition Thuban 3.2GHz
COOLING - I installed Corsair H2O cooling, I wanna say the Corsair h70 series?
G-Card - 2 Xfired Radeon HD 6870 1GB 256-bit DDR5
PSU - CORSAIR TX Series CMPSU-750TX 750W ATX12V v2.3 SLI Ready CrossFire Ready
RAM - G.SKILL Ripjaws X Series 8GB (2 x 4GB) DDR3 SDRAM DDR3 1600 (I have two open slots on the MoBo still)
HDD - 1 HITACHI Deskstar 2TB 7200 RPM (this is the one I have games installed on, so a new SSD for gaming purposes is a valid suggestion. Though tbh, it is not really load times I am concerned with) (I also have a few other irrelevant HDDs)
SSD - OCZ-VERTEX2 128GB (this one has Windows and nothing else, besides the stuff that gets added automatically, like game saves in MyDocuments. It has 32GB free)
INTERNET - I am supposed to have 50 MB/s coaxial internet, but my speed tests usually hover right around the 20MB/s mark. Just to say, upgrading my internet is not out of the question if it would be best for MMO purposes.
MODEM - Linksys CM100 (still a docsis 1.0 modem)
ROUTER - LinkSys E2000, but I use an Ethernet connection, leaving wireless disabled on the PC I game from

I probably have the latest GPU drivers and version of Catalyst Control Center, as I updated it about 2 months ago. I will probably check that again now to be sure.
At that time, I also installed the AMD Gaming Evolved optimizer software that comes with the latest CCC. I let it install and run for now, because I have not really heard anything bad about it yet.
I have no overclocking. I know I probably have the parts for it, so feel free to include that in any recommendation (no need to give detailed steps if so, just any suggestion. I can do the work to OC myself)

Hmm, that is all that I can think of that could be relevant. But let me know if I missed anything.
Also, if anything is in desperate need of an upgrade, regardless of price, please point that out.

Thanks

edit - If possible, I would also like to hear what kind of improvements I might reasonable expect for any suggestion made.

 

[jsgrant31]

I think a better GPU would give you the best performance boost. A single 280x and you're likely approaching 60 fps on ultra. After that, my next upgrade would be a new mobo and an Intel Skylake CPU. Your CPU should be more than sufficient for ESO though, and your other components are fine too.

 

[MPWB]

R9 280x is a great card, and you will most likely get performance in the 60fps region with most games. Other than that you could just save up for another build.